System Clock, clock speed, Word Length & Bus Width

System Clock, clock speed, Word Length & Bus Width

System Clock

A quartz controlled oscillator that supplies a timing signal at a fixed rate. It could be likened to someone clicking their fingers, everything happens at this rate.

Every computer has its own systems clock.

System Clock, clock speed, Word Length & Bus Width

System Clock

The data and instructions are fetched, decoded and executed in time with the system clock.

Instructions and data are processed in time to the system clock.

Instruction Data Data Instruction Data

1 Hz 2 Hz 3 Hz 4 Hz 5 Hz

A typical clock speed or clock frequency: 2.4 GHz

(2400,000,000 cycles per second)

Clock speed of the processor

System Clock, clock speed, Word Length & Bus Width

System ClockInstructions and data are processed in time to the system clock.

Instruction Data Data Instruction Data

1 Hz 2 Hz 3 Hz 4 Hz 5 Hz

2.4 GHz(2400,000,000 cycles per second)Processor

Internal Bus

MemoryWhen transferring data or instructions between the processor and main memory, sometimes the internal bus speed slows a computer down.

System Clock, clock speed, Word Length & Bus Width

Word LengthData is transferred in binary words. These represent the data and instructions in a computer system.

1 0 1 0 1 0 1 0(x8 bit binary word)

Internal Bus

Word Length

1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0

1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0(x16 bit binary word)

(x24 bit binary word)

W

System Clock, clock speed, Word Length & Bus Width

Bus WidthBus width refers to the number of signal wires or lines allocated to a bus.

Direction of travel

The number of lines in a bus

What is the effect of bus width on binary word size?

System Clock, clock speed, Word Length & Bus Width

Bus Width The effect of bus width on word size

No. Of wires in bus

No. Of bits in a word on the bus

No. Of different binary words

No. Of different binary words as a power of 2

Example of a binary word on the bus

The largest word counting in denary

1 1 2 21 1 1

2 2 4 22 10 3

3 3 8 23 101 7

4 4 16 24 1100 15

8 8 256 28 11110001 255

16 16 65,536 216 1101101111110000

65,353

20 20 1,048,576 220 ... 1,048,575

24 24 16,777,216 224 ... 16,777,215